Syndecans, cell surface heparan sulfate proteoglycans, (HSPG) bind and modulate the activity of a large number of extra-cellular effectors. The ectodomains of the syndecans can be shed, generating soluble HSPGs that can inhibit these cell surface interactions. Several transgenic mouse lines that express high levels of cell surface syndecan- 1 under the control of a CMV promoter/enhancer were generated to evaluate its functions in vivo. Syndecan- 1 was expressed in multiple somatic tissues and in the hypothalamic areas that regulate body weight. The transgenic mice mimic (i) obese mice with abnormalities in melanocortin-4 receptor function and (ii) humans with the Bardet-Biedl syndrome, a genetic malformation and obesity syndrome of unknown etiology. Transgenic expression of syndecan- 1 appears to have has uncovered a physiological control of feeding behavior. These studies define new functions for syndecans and have important implications for understanding eating disorders, both obesity and cachexia. Obesity is a significant public health hazard; about half of U.S. women and men are now considered overweight and the IOM indicates that this costs more than $70 billion annually in the U.S. Thus, syndecan induction and syndecan interactions are potentially important new targets for pharmacological control of body weight. Specifically, the investigators aim to explore the remarkable phenotypes produced by syndecan- 1 overexpression: (i) establish the role of syndecans in melanocortin receptor function by characterizing the interaction of syndecans with agouti/AGRP peptides and analyzing how this interaction modulates melanocortin receptor signaling both in vitro and in vivo. (ii) evaluate whether hypothalamic expression of syndecan-3 is a physiological regulator of feeding behavior by characterizing the induced expression of hypothalamic syndecan-3. analyzing feeding behavior in syndecan-3 null mice and identifying potential regulators of hypothalamic synce~an-3 expression. (iii) analyze the obesity and morphogenetic abnormalities of the syndecan- 1 overexpressing mouse by evaluating the mouse as a genetic model of the Bardet-Biedl syndrome and by identifying the genes responsible for morphogenetic abnormalities and for reducing the obesity.